Colicin E4

Colicin E4 is a type of Colicin, a bacteriocin made by E. coli which acts against other nearby E. coli to kill them with its 16s rRNase activity; it digests the 16s ribosomal subunit, ultimately leading to the death of the cell.

Synthesis and release
The colicin E4 operon is encoded on a plasmid in E. coli, alongside a regulatory protein, and its Colicin Immunity Protein, Im4.

Mechanism of uptake
Colicin E4 binds first to the vitamin B12 BtuB outer membrane receptor on the target cell, via its receptor binding domain. Binding to this receptor triggers the immunity protein to release from the cytotoxic domain, so that when the colicin crosses the membrane it can kill the cell. Once bound to the BtuB receptor, ColE4 uses OmpF and the TolQRAB complex to cross the membrane, using a mechanism as yet unidentified.

Killing Activities
ColE4 kills the target cell with its 16s rRNase activity where it enzymatically degrades its 16s rRNA subunit, and inhibits protein synthesis in the cell. This ultimately leads to the death of the cell.